Editor's note: Julian E. Zelizer is a professor of history and public affairs at Princeton University's Woodrow Wilson School. His new book, "Arsenal of Democracy: The Politics of National Security -- From World War II to the War on Terrorism," will be published this fall by Basic Books. Zelizer writes widely about current events.

Julian Zelizer says opponents have mobilized the public to block health reform for 60 years.

PRINCETON, New Jersey (CNN) -- One of the great puzzles this summer has been why President Obama seemed to have underestimated the intensity of the counter-mobilization he would face in proposing health care reform.

Historically, each time an American president has sought to reform the health care system, opponents mounted a fierce and unrelenting attack to undermine public support.

President Harry Truman confronted such an attack after his dramatic upset against Republican Thomas Dewey in 1948. Truman proposed national health care as part of the "Fair Deal." The American Medical Association instantly branded the proposal "socialized medicine." It hired a public relations firm, Whitaker and Baxter, for $1.5 million in 1949.

The firm employed a variety of tactics, sending out speakers to drum up opposition and distributing information to the press. One of their pamphlets asked: "Would socialized medicine lead to socialization of other phases of American life?" The mobilization worked. Public approval plummeted from 58 percent to 36 percent.

Similar charges were leveled against Presidents John Kennedy and Lyndon Johnson's Medicare proposal between 1961 and 1965. When Kennedy first announced his plan to provide health care to the aged, the AMA's bi-weekly publication compared the fight over this proposal to the "struggle to prevent the spread of incipient cancer."

They warned that, "The Socialist Party in the United States has launched a nation-wide campaign for socialized medicine in America and has made it clear it supports President Kennedy's proposal for health and medical care through the Social Security system as the vehicle with which to bring full-blown socialized medicine to this country."

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According to Johnson biographer Randall Woods, the AMA hired 70 publicists and 23 lobbyists, spending over $50 million. Local activists in the budding conservative movement also included Medicare as one of the main issues in their litany of warnings about how both administrations were promoting a communist government here in America.

The same thing happened to President Bill Clinton. After he released his plan, the Health Insurance Association of America, which represented small insurance companies, released a blistering "Harry and Louise" spot that shook public opinion. The ads showed a married couple sitting around the kitchen table saying how they were scared and confused about what the legislation would do.

The Coalition for Health Insurance Choices, an alliance of opponents of health care, worked with local business leaders to apply pressure to legislators and they organized letter-writing campaigns to members of Congress as well as to local newspapers.

The National Federation for Independent Business conducted a massive campaign against the proposed employer mandate. They sent out "fax alerts" to business owners, urging them to write members of Congress. The NFIB also conducted seminars around the country and paid for ads against legislators who supported Clinton's plan.

Republicans used the legislation as a focus for the 1994 midterm campaigns. The neoconservative William Kristol sent a series of memos to Republicans urging them to use this debate to define themselves as the party of free markets and opposition to the welfare state. "Sight unseen," he wrote, "Republicans should oppose it."

The Wall Street Journal published a piece by Republican Richard Armey called "Your Future Health Care Plan" in which he branded the Clinton plan as "a bureaucratic nightmare that will ultimately result in higher taxes, reduced efficiency, restricted choice, longer lines, and a much, much bigger federal government." Grassroots conservative organizations, including the Christian Coalition, enlisted their supporters by paying for postcards, radio commercials, as well as print and television ads.

When the Clinton administration launched a national bus tour to build grassroots support in the summer of 1994, when the legislation was stalled in several congressional committees, it could not escape the opponents.

During the first stop in Portland, Oregon, the Clinton entourage arrived to find a broken-down bus that conservatives had wrapped up in red tape. This was meant to symbolize the government bureaucracy. The protests, organized by the Citizens for Sound Economy, continued to follow the administration's caravan wherever it went.

When Hillary Clinton, who took the lead on the health care proposal during the Clinton administration, spoke to a group in Seattle, Washington, she was confronted by hundreds of angry, yelling protesters, who had been urged to attend by local radio talk show hosts. The protesters accused her of everything from promoting socialized medicine, to seeking to expand abortion rights, to wanting to take away people's guns. The protesters surrounded her limousine as she tried to leave.

This time around there was so much attention on how President Obama would handle Congress -- whether he should mimic the Clinton approach by giving legislators a complete bill or act more like Lyndon Johnson by granting Congress autonomy to shape the program themselves -- that it seems the White House didn't pay sufficient attention to the battle over public opinion.

It is doubtful that the administration would have been able to temper the protests that took place. But had the White House better mobilized its large base of supporters from the campaign, it might have offered a stronger local response in communities to the town hall protesters who have been dominating the discussion.

Just as important, President Obama could have done more himself by using the bully pulpit of the presidency to explain the basic components of his vision for health care reform. In August, Obama paid the price for failing to do so.

There is still time for the president to salvage health care reform, though it will be difficult. After all, Lyndon Johnson came out from the fight victorious. The first two weeks of September will be absolutely crucial to determining whether the president can win back public opinion or whether he will join the long list of presidents who have been stung when sticking their hands in this political beehive.

The opinions expressed in this commentary are solely those of Julian Zelizer.